Microphone



June 27, 1944. J ANDERSON 2,352,305

MICROPHONE Filed Jan. 2, 1941 Zmnentor Leslze Jflnderaon (Zttorneg Patented June 27," 1944 MICROPHONE Leslie J. Anderson, Haddonfield, N. J assignor to Radio Corporation of America, a corporation of Delaware Application January 2, 1941, Serial No. 372,753

7 Claims.

This invention relates to microphones of the dynamic type, and more particularly to the acoustic labyrinth employed in connection with pressure responsive microphones, the present invention being an improvement over that disclosed and claimed in the copending application of Harry F. Olson, Serial No. 270,801, filed April 29, 1939 and assigned to the RadioCorporation of America.

In the said copending application there is disclosed a microphone having a pressure responsive element and a pressure gradient responsive element, the former terminating in an acoustic labyrinth constituted by a-solid member having a plurality of longitudinally extending bores therethrough which are serially connected to provide a long, continuous passage. This labyrinth is filled with suitable damping material, such as loosely packed hair felt, or the like, in order to simulate the effect of a loading pipe of infinite length.

In assembling the structure shown in the aforementioned copending application, care must be exercised to uniformly distribute the damping material throughout the labyrinth. Furthermore, while the arrangement disclosed in said application is highly satisfactory in use, it does not lend itself to the greatest economy.

The primary object of my present invention is to provide an improved labyrinth structure which will not be subject to the aforementioned objections.

More particularly, it is an object of my present invention to provide an improved labyrinth for pressure responsive microphones which is inexpensive in cost, easy to manufacture, substantially free from leakage and highly eiiicient in use.

Another object of my present invention is to provide an improved labyrinth as aforesaid in which the loading material is uniformly distributed throughout the labyrinth.

Another object of my present invention is to provide an improved labyrinth as aforesaid which readily lends itself to quantity manufacture in great economy, and which can readily be assembled with precision even by one unskilled in the art.

According to one form of my invention, I form the acoustic line or labyrinth by a plurality of thin slabs or disc-like members, each provided with an equal number of openings, and assemble them alternately with layers of silk. The openings in each of the slabs or discs are arranged in axially aligned relation to provide a plurality of parallel, axially displaced, discrete passages, these passages being serially connected to provide a continuous, long passage. The silk layers in between each of the discs or slabs constitute the acoustic resistance evenly distributed throughout the continuous passage.

In another form of my invention, I omit the silk layers in between the discs and insert into each of the passages a tubular member of paper or the like which has been rolled up with uniformly distributed hair felt or similar material to simulate the well known cigarette. After the discs are assembled, these individual tubes can be quickly inserted, one into each of the discrete passages, after which suitable end members are applied to the assembly to serially connect the several passages. Of course, if desired, the labyrinth may be made of a single solid member, as disclosed in the aforementioned Olson application, and the tubular members constituting this phase of my invention may be inserted into the discrete bores thereof.

The novel features that I consider characteristic of my invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and method of operation, as well as additional objects and advantages thereof, will best be understood from the following description of several embodiments thereof, when read in connection with the accompanying drawing, in which:

Figure l is a view, partly in elevation and partly in section taken along the line II of Fig. 2, of a microphone including a labyrinth constructed according to one form of my invention, the microphone casing being shown in section and the labyrinth being shown in elevation.

Figure 2 is a top plan view of this form of labyrinth with the top end section removed,

Figure 3 is an enlarged, detail, sectional view taken on the line III-III of Figure 1,

Figure 4 is a perspective view of one of the tubular members filled with damping material and made in accordance with the second form of my invention,

Figure 5 is an end view thereof, and

Figure 6 is a fragmentary sectional view of an acoustic labyrinth formed of solid material and including the damping material according to the second form of my invention.

Referring more particularly to the drawing, wherein similar reference characters indicate corresponding parts throughout, there is shown, in Fig. 1, a conductive, vibratile member I, such as a crimped aluminum ribbon, arranged to vibrate in an air gap between a pair of pole pieces 3 (only one of which is shown) to which flux is supplied by a magnet 3. Behind the ribbon i is a pipe 1 which leads to and communicates with an acoustic labyrinth according to the first form of my invention, the structure thus far described being supported on a plate 9.

The acoustic labyrinth of this form of my invention is constituted by a plurality of disc-like members or slabs l3 each of which is provided with a plurality of axially-spaced openings Ii, l1, l3, 2|, 23, 25, 21, 23, 31, 33, 35 and 31, and also with a peripheral notch 33. To one surface of each of the discs I3 is secured a layer of foraminous material 4i, such as silk, as by means of a suitable adhesive, the material 4| in each layer covering the openings in the disc II to which it is secured. The labyrinth also includes top and bottom end members 43 and 43, the former being provided with an opening 41 by means of which. communication is established between the pipe 1 and the labyrinth, as well as a plurality oi recesses 49, ii, 53, 55 and 51. The

' bottom end member 45 is similarly provided with a plurality of recesses 53, 3|, 63, 65, 31 and 63.

In assemblylng the labyrinth, the bottom end section 46 is first inserted into the casing Ii, after which a suitable number of members l3 with attached silk layers 4| are also inserted into the member I I, and finally the top end member 43 is' placed on the uppermost disc i3, face down, after which the plate 9 is placed on the end member 45. A ring member 46, which is threadedly received in the casing ii, is then screwed down tight against the top end member 43 to hold the assembly in place. A keyway 1| on the cylindrical member ll cooperates with the peripheral slots 3| in the members I3, 43 and 45 to insure their being aligned in such a manner that the respective openings of the discs I! are in axially aligned relation to thereby provide continuous, parallel, axially-spaced, discrete bores or passages. When so assembled, the pipe 1 communicates with the top of the passage constituted by the aligned openings i5 through the opening 41 in the top end member and a superposed, aligned, opening 43 in the supporting plate 3. At the bottom of the passage constituted by the openings 15, the recess 59 in the end plate 43 serves to connect that passage with the next following passage constituted by the aligned open ings l1.' Thereafter, the recess 49 in the end member 43 connects the tops of the passages constituted by the respective openings i1 and iii. The bottom of the passage constituted by the openings i9 is connected by the recess 6i with the bottom of the passage constituted by the aligned openings 2|, and so on serially through all the openings until, finally, the labyrinth is terminated at the top end of the opening 31. The leads 13 and 16 from the ends of the ribbon I may be brought down through a series of aligned openings 11, also formed in the discs l3 and in the end members 43 and 45, and through the bottom of the cylindrical member Ii to an output transformer 13.

In Figs. 3, 4 and 5, I have shown a somewhat different form of my invention wherein the accustic resistance is constituted by a tubular member 3| of thin paper or the like which is rolled up to enclose uniformly distributed hair felt or like material 33, similarly to the conventional cigarette. The labyrinth may be made up of a number of discs and end members, as in Fig. l,

with the silk layers 4! omitted, or it may be made in one, integral, solid piece, as disclosed in the aforementioned Olson application. In any case, a tube 3i with the enclosed damping material 33 is inserted in each of the discrete, longitudinal passages of the labyrinth to substantially fill each of said passages. It is obvious, that the damping material 33 can be much more uniformly distributed in the paper sheet ll prior to rolling thereof than when inserted by hand into the longitudinal passages of the labyrinth, as is now customary. Moreover, after fabrication, the tubes II can be very easily slipped into each of the longitudinal passages of the labyrinth.

Although I have shown and described two embodiments of my invention, it will be apparent to those skilled in the art that other modifications, as well as changes in those described above, are also possible. Furthermore, the precise method of assembling the labyrinth need not be as described above. For example, if desired, the end members 43 and 45 and the intermediate discs l3 with the alternated silk layers I3 may b first assembled by applying a suitable cement to both surfaces of the discs l3 and bonded together under heat and pressure, if necessary, into a solid unitary mass prior to insertion into the casing l i. This method may be followed advantageously where, for example, the members I3, 43 and 4| are made of a thermoplastic material instead of out of cardboard, fibre, or similar material. I therefore desire that my invention shall not be limited except insofar as is made necessary by the prior art and by the spirit of the appended claims.

I claim:

1. An acoustic labyrinth for a pressure responsive microphone comprising a plurality of disclike members each having a plurality of openings extending therethrough, said members being assembled in superposed relation into a unitary structure with their respective openings in axially aligned relation.

2. An acoustic labyrinth for a pressure responsive microphone comprising a plurality of disclike members each having a plurality of axiallyspaced openings extending therethrough, said members being assembled in superposed relation into a unitary structure with their respective openings in axially aligned relation whereby to provide a plurality of axially-spaced, discrete passages, and means serially connecting said passages into one continuous passage.

3. An acoustic labyrinth for a pressure responsive microphone comprising a plurality of disclike members each having a plurality of axiallyspaced openings extending therethrough, said members being assembled in superposed relation into a unitary structure with their respective openings in axially aligned relation whereby to provide a plurality of axially-spaced, discrete passages extending longitudinally through said structure, means serially connecting said passages into one continuous passage, and means associated with said discrete passages affording an acoustical resistance therefor.

4. The invention set forth in claim 3 characterized in that said last named means is constituted by layers of foraminous material extending across said discrete passages.

5. The invention set forth in claim 3 characterized in that said last named means is constituted by layers of foraminous sheet material interposed between and alternated with said disclike members.

6. The invention set forth in claim 3 characterized in that said last named means is constituted plurality of discrete passages extending longiby a plurality of tubular members filled with tudinally therethrough, means serially connecting acoustic damping material, one each of said tubes said passages into one continuous passage, and a being inserted in one each oi said discrete pastubular member filled with substantially evenly sages and substantially filling said passages. 5 distributed acoustic damping material in each of 7. An acoustic labyrinth for a pressure responsaid discrete passages.

sive microphone comprising a member having a LESLIE J. ANDERSON. 

